I am 17 weeks and didn't even know that it mattered until I saw a couple of threads on MN. I was sleeping on my back but was told that it restricts the oxygen to the placenta. I then started sleeping on my side but saw a fetal movement thread on here that said that you are supposed to sleep on your left side again because of oxygen and the placenta. I then saw a different one that said it is better to sleep on your right side. Does anyone know anything about this or even if it matters. Thanks.